A known apparatus of this type is described in an article entitled "Optical consequences of blood substitution on tissue oxidation-reduction state microfluorometry" (by Shigeki Kobayashi et al) published in the United States magazine "Journal of applied physiology", vol 31, No 1, June, 1971. Said apparatus uses a radiation source which includes a mercury vapour lamp and filters. Said source is capable of illuminating an organ at two different wavelengths--an ultraviolet wavelength (366 nm) and a red wavelength (720 nm). Illuminating an organ at an ultraviolet wavelength causes fluorescence (at 440 to 480 nm) which is picked up by a photoelectric receiver.
The organ reflects part of the incident red energy in a reflected beam which is picked up by another photoelectric receiver. Said apparatus further includes a system for recording the output signals of the two receivers.
The measured intensity of the fluorescence is representative of the oxidation-reduction state of the organ.
However, variation in intra-tissue concentrations of red blood corpuscles disturbs the photometric measurements, in particular when experiments are made in situ in a living organ. It particular, a reduction of said concentration of red blood corpuscles causes an increase in the fluorescence recorded.
The variations in intensity of the reflected red radiation are representative of the intra-tissue concentration of red blood corpuscles.
By operating on an organ kept at a constant oxidation reduction state, by means of the apparatus described in said article, Kobayashi was able to draw graphs and to establish an equation relating fluorescence intensity to red reflection intensity obtained firstly on an organ emptied of its blood and secondly on an organ which contained varying quantities of red blood corpuscles. Kobayashi considers that the results obtained during his study show that it is possible to electronically compensate the variations in fluorescence as a function of the intra-tissue concentration of red blood corpuscles.
The apparatus described in said article therefore allows the NADH/NAD ratio to be studied over full, slow and provoked variations during experiments which can only be carried out in a laboratory on an isolated and artificially perfused organ separated from the system to which it belongs and therefore on a model which is far removed from its physiological state.
Preferred embodiments of the present invention provided apparatus for studying low-amplitude variations which are rapid (especially during a single cardiac cycle), spontaneous and/or provoked of the NADH/NAD ratio on an organ which is not separated from the system to which it belongs, said organ being normally perfused with blood in a physiological situation, in particular by simple tapping intravascular catheterization or endoscopic examination, said apparatus being designed for clinical applications, in particular during surgical operations.